The present invention relates to a Variable Reluctance resolver (VR resolver) having a zero point detector, and in particular a VR resolver that is capable of accurately and reliably detecting a zero point of a resolver rotor by detecting multiple detection portions provided on the rotor.
A conventional VR resolver is effective as an incremental rotation sensor because a resolver output signal, which includes the sine signal and cosine signal output from a resolver output winding, is output n times per one revolution of the resolver rotor. FIG. 5 shows the correlation between an electrical zero point signal, the resolver output signal and the resolver angle with the axis combination angle nX, where nX=360°.
As graphically shown in FIG. 5, in a conventional resolver for which the axis combination angle nX is 2× or greater, detection of the absolute angle position cannot be executed because the same resolver output signals are repeatedly output n times per revolution of the resolver rotor. To solve this problem, an exemplary VR resolver having a zero point detector has been proposed.
FIGS. 6A–6B are explanatory drawings that show a conventional VR resolver having a zero point detector. In FIG. 6A, the zero point detector 101 of the conventional VR resolver has an excitation winding 103 and an n-phase output winding 104 on the ring-shaped stator 102. A rotor 105 is an iron-only core and is installed so that it can freely rotate relative to the stator 102. The gap permeance with the stator 102 is formed in a partial circle so that the shape of the sine wave portion of the resolver output signal varies relative to the rotation angle θ. A detection portion 107 formed in the rotor 105 is defined as a concave portion in the rotor 105, and a zero point detection winding 106 is located on the stator 102.
The zero point detector 101 detects the position of the detection portion 107 based on the output voltage, or zero point detection signal, Vx′ that is output from the zero point detection winding 106. The zero point detection signal Vx′ is, as shown in FIG. 6B, generated by and output from the zero point detection winding at the zero point of the rotation angle as the detection portion 107 rotates past the zero point detection winding 106. An example of such a conventional VR resolver is described in Japanese Patent Application 2000-258187.
Further regarding the above-described zero point detector 101, the zero point detection winding 106 is provided on a magnetic pole of the stator 102. As the rotor 105 includes only one detection portion 107, the zero point detection winding 106 only outputs the zero point detection signal Vx′ for the rotation angles 0° and 360°.
The above-discussed VR resolver has an associated axis combination angle of 1×. When the axis combination angle is 2× or greater, a counter can be used to measure the zero point detection signal Vx′. As shown in FIG. 5, electrical zero point signals are output one at a time from 1 to n for every section where the sine and cosine output voltage signals of the sine winding and cosine winding complete one cycle, for example, every section of 1×, 2× . . . nX. The “1” point of the electrical zero point signal with respect to a count value of the counter occurs at the absolute angles 0° and 360°. However, as the counter measures 1 to n of the electrical zero point signals and converts these signals to an absolute angle, the absolute angle cannot be detected when the count value of the counter is lost due to an error such as a detection error. This is because the counter measures only one electrical zero point signal.
To overcome the above design limitation, a resolver such as that disclosed in Japanese Patent Application 2001-197610 may be connected in a redundant manner so that it operates accurately even if a detection error occurs. However, such a resolver is impractical from an implementation standpoint because it requires approximately twice the number of parts and configuration space compared to a resolver that does not include such a redundant connection.
Therefore, what is needed is a VR resolver with a rotor that has magnetic poles with 2× or greater axis combination angles, and that is structured to carry out accurate and reliable detection of a zero point detection signal.